The Fifteenth Gordon Research Conference on Fertilization and the Activation of Development will provide a forum for presentation and discussion of new developments and ideas in this exciting, rapidly advancing field. This meeting will be held at the Holderness School, Plymouth, New Hampshire, July 27 - August 1, 2003. This conference has been held every two years since 1974. It is the only Gordon Research Conference concerned with the interaction of the male and the female gametes in the vital process of fertilization and activation of the fertilized egg to begin the process of embryo formation. It provides a venue for the interaction of biochemists, cell biologists, molecular biologists, physiologists, geneticists and biophysicists working in the field. This conference has been singularly successful in fostering collaborations among scientists with widely disparate experience and seniority and, among research laboratories in this country and in Europe, Japan, Australia and Latin America. These collaborations have borne many fruitful results. There will be nine sessions in the conference, following the Gordon Research Conference format. Eight sessions will focus on: 1) Alternative reproductive strategies; 2) Sperm-egg interactions; 3) Sperm signal transduction; 4) Sperm-egg membrane interactions; 5) Events of egg activation; 6) Paternal effects on development; 7) Maternal effects on development; 8) Establishment of embryonic polarity. These sessions will include both scheduled speakers, as well as selected short talks chosen from posters and/or late breaking topics. These latter talks will particularly feature junior scientists, including postdoctoral fellows and students. In addition, we will have a keynote speaker for the Tuesday evening session.